PROJECT SUMMARY This F31 research and training award will enable the candidate to develop as a public health researcher using advanced methodology and statistical techniques to examine person- and event-level determinants of substance use. Alcohol and marijuana are two of the most commonly used substances among young adults, and most individuals who use both substances use them simultaneously (in the same occasion so their effects overlap). Simultaneous alcohol and marijuana (SAM) use, compared to alcohol or marijuana use alone, is associated with more frequent and intense alcohol use, and a greater number and severity of alcohol-related consequences. Given the high prevalence and adverse effects of SAM use, identification of proximal predictors of SAM use among young adults is important for informing prevention and intervention efforts. The Integrated Behavioral Model (IBM) provides a framework for understanding SAM use by highlighting important psychosocial (attitudes, norms) and contextual (e.g., social context) predictors. The overall aims of the research proposed in this F31 are to characterize event-level SAM use and examine IBM-informed pathways of SAM use among heavy drinking young adults, using a mixed methods approach. First, qualitative methods (individual interviews with 20-28 heavy drinking young adult SAM users) will be used to (a) elucidate topography and proximal antecedents of SAM use among young adult heavy drinkers and (b) inform event-level assessment decisions for an ecological momentary assessment (EMA) protocol for studying discrete substance use events. Subsequently, this F31 application will build upon an NIAAA-funded R01 EMA study (R01AA027495) examining high intensity drinking and alcohol induced blackouts among young adults. The candidate will add SAM-specific measures to one of the R01?s panel assessments and subsequent 30 day EMA burst. Using the first 100 participants who engage in frequent SAM use, the candidate will analyze direct effects of person- and event-level predictors of SAM use, and examine event-level mediators and moderators of the association between psychosocial predictors and SAM use among young adult heavy drinkers. The candidate will work with a highly skilled mentorship team (Drs. Jennifer Merrill, Kristina Jackson, and Kate Carey) at Brown University?s Center for Alcohol and Addiction Studies to build four areas of expertise relevant to this research agenda: (1) content area knowledge of SAM use among young adults; (2) qualitative methods and analysis; (3) EMA methods; and (4) analysis of EMA data. This F31 proposal to understand determinants of SAM use will help to identify intervention targets for young adults who are at high risk for substance misuse and related consequences, and will position the candidate to make important contributions to the field of substance use research.